I believe you can via phone but you should be able to do it free of charge in your self serve online to the best of my knowledge. If you need a different area code though you will most likely have to call *611

There is a fee of $25 to change your number. With what you mentioned, the fee would be legit. BUT since it seems you are a new customer, they might be able tio give you a one time credit. You could also log into self serve and change your number there too.

It is free if you do it through self serve. It will cost you $25 if you call in and agent change the number for you.
Log into self serve > Mobile phone > Change phone number > option 1 "I need a new mobile phone number" and follow instructions.

It's $25 if you can't get the rep on the phone to waive the fee for you by acting dumb or being nice. You can always hang up and talk to someone else.
This will work 99.99% of the time: I'm getting calls/messages from numbers I don't know. I think you gave me a previously used number and I can't change it through self-serve!